Of all the alternative routes to enter teaching, few are as well known as Teach for America. The program recruits top-flight candidates from prestigious universities across the United States, and the statistics are impressive: This year, 15 percent of Yale's seniors and 16 percent of Princeton's applied, as did 25 percent of all African-American seniors at Harvard.

TFA has passionate supporters who believe it can help transform education in the US, as well as vehement detractors who dismiss it as promoting a sort of Peace Corps experience rather than recruiting more-permanent teachers.

The program consists of an intense five weeks of training, after which graduates commit to teaching two years in urban classrooms. While serving as TFA teachers, they also undertake university course work and receive coaching. The program started in 1990, and 20,000 people have gone through it.

Kilian Betlach became a TFA teacher in 2002, teaching language arts to students learning English in a middle school in East San Jose, Calif. His five-week training was targeted to the sort of setting he was teaching in, and since his experience, the training has improved, he adds. But he doesn't believe it can ever truly prepare teachers for what they'll face that first year.

"You need that specificity [for urban learning] that TFA offers, but you certainly need more time," says Mr. Betlach. "One of the things you see with the demands of learning as you go – they take a lot out of you. You see people coming out in [their second and third years] and being effective, but the effort and emotional toll it takes is one of those things that speaks against longevity."

Betlach and his three TFA roommates, for instance, started what they called the "4 o'clock club" – regularly waking up at 4 a.m. to work on lesson plans and prepare for the day.

Still, Betlach stayed for six years – longer than many TFA teachers. And he's an example of a trend that TFA proponents often cite: He has gone on to a career in education, working for the policy group Education Trust-West in Oakland, Calif., which would have been unlikely without the TFA experience, he says.

TFA points to recent studies showing that its graduates are, in fact, effective even in that first year. It also says that one of its goals is to train people who can help transform the education and urban-poverty landscape overall – a task that doesn't necessarily require their graduates to remain in the classroom for many years. Only about 30 percent of TFA alums are still teachers, but two-thirds are involved in education, says Kevin Huffman, TFA's head of public affairs.

"We explicitly view our work as ... ensuring that teachers have a tremendous impact on the students they reach, but we're also trying to build a human-capital pipeline for leadership," Mr. Huffman says.